This invention relates to tuning voltage controlled oscillators, and in particular to automated tuning of a voltage controlled oscillator using a wire bonder to precisely establish the frequency of operation of the voltage controlled oscillator.
Voltage controlled oscillators often have a tuning stub that is used to fine-tune the frequency of operation of the voltage controlled oscillator. A stub is employed to establish the frequency of operation of the voltage controlled oscillator. A stub short placed across conductive runners of the stub determines the frequency of operation of the voltage controlled oscillator. Prior techniques placed a stub short at a location along the stub that produced approximately the desired frequency of operation of the voltage controlled oscillator. The voltage controlled oscillator was powered and tested to determine the frequency of operation due to the presence of the stub short. The position of a second stub short relative to the first stub short was determined that would result in the desired frequency of operation of the voltage controlled oscillator. The position of the second stub short was manually measured relative to the first stub short and manually bonded along the stub to fine-tune the frequency of operation of the voltage controlled oscillator. The voltage controlled oscillator was again powered and the frequency of operation of the voltage controlled oscillator resulting from the presence of the second stub short was determined. If the second stub short, which was manually positioned along the stub, resulted in the desired frequency of operation of the voltage controlled oscillator, the fine-tuning was concluded. However, if the second stub short was not precisely positioned along the stub, the frequency of operation of the voltage controlled oscillator was not at the desired frequency, the second stub short may have to be removed, and the process was repeated to fine-tune the frequency of operation of the voltage controlled oscillator.
A shortcoming of the prior art technique was that the position of the second stub short was manually measured along the stub and manually secured, such as by soldering or thermosonic welding, in place. The stub short, which is often a wire, may require being positioned with an accuracy that is less than the diameter of a cross section. Since the frequency of operation of the voltage controlled oscillator is dependent on precise positioning of the stub short along the stub, any deviation from the position that would result in the desired frequency of operation would cause the voltage controlled oscillator to operate at an undesired frequency of operation. In such cases, the stub short may have to be removed and another attempt to position and secure a short stub undertaken to establish operation of the voltage controlled oscillator at the desired frequency of operation. Such iterative steps are very costly.
Thus, what is needed is a technique for precisely positioning a stub short along a stub for tuning a voltage controlled oscillator such that precise positioning of the stub short results in the desired frequency of operation of the voltage controlled oscillator. Such a technique would reduce the cost of fine tuning the voltage controlled oscillator.
In accordance with the invention, fine tuning the operation of a stub tunable device includes placing a first stub short across conductive runners of a tuning stub at a distance preferably greater than a distance resulting in the desired tuning dependent variable of the stub tunable device. Thereafter, the stub tunable device is powered and tested to determine an initial tuning dependent variable of operation of the stub tunable device. The position of a second stub short is determined based on the tuning dependent variable of the stub tunable device due to the presence of the first stub short, the geometry of the tuning stub and the desired of the stub tunable device. A second stub short is precisely positioned along the stub using automated equipment, relative to the position of the first stub short, to result in the desired tuning dependent variable of the stub tunable device. Depending on the relative positions of the first and second stub shorts relative to the stub tunable device, the first stub short may be removed. Only the stub short that results in the shortest stub length influences the tuning dependent variable. Should the second stub short require being located along the stub to result in a longer stub, then the first stub short must be modified, such as being severed or removed, so as not to influence the tuning dependent variable. The stub tunable device may again be powered and tested to confirm the desired tuning dependent variable of the stub tunable device.